1. Field of the Invention
This invention relates to a process for the preparation of urea-formaldehyde based fertilizer compositions for the foliar feeding of plants.
2. Description of the Prior Art
Fertilizers containing nitrogenous compounds capable of releasing their nitrogen content by microbial action for the feeding of plants, particularly turf grass, have been extensively utilized for many years. Besides extending the feeding process over a period of time, a further important advantage afforded by this type of fertilizer is the freedom from burn damage to the plant even when the fertilizer is applied under unfavorable climatic conditions. The first commercial fertilizers of this type were derived from organic waste products such as the sludge produced in an industrial sewage treatment operation. These products, however, commonly suffer in that they are objectionably odorous, tend to be dusty and possess a very low nitrogen content.
By far the predominant bulk of the so-called slow release fertilizers being marketed currently are granular products wherein the nitrogen content is in the form of the partial condensates of urea and formaldehyde. The general method for preparing these condensates consists of initially effecting the formation of mono- and dimethylol ureas under relatively high basicity conditions followed by reacting the methylol ureas under acid conditions to promote the formation of methylene urea polymers. Products of this type by nature of the underlying condensation reaction inevitably contain free urea which in the fertilization process is quickly available for feeding purposes. Thus, there is no substantial lag period in the feeding process as experienced in the use of the natural organic products. The lower methylene urea polymers, on the other hand, while initially water insoluble degrade in time by microbial action to generate assimilable nitrogen compounds. The foremost difficulty experienced in preparing such fertilizer compositions in a commercial sense is that of limiting the formation of the high molecular weight methylene urea polymers. The higher methylene urea polymers are essentially inert components in that only an exceedingly small percentage of their nitrogen contents ever become available for feeding purposes.
As indicated, the urea-formaldehyde based fertilizers have been primarily developed for use in a solid form. Therefore, the utilization of such materials for foliar feeding applications has hitherto been essentially a compromise proposition. In this connection it has been proposed to employ aqueous suspensions of the urea-formaldehyde partial condensation products for this purpose. However, this approach gives rise to a number of problems. For one, a stable suspension having a reasonably high nitrogen content; e.g., 10-12%, is difficult to prepare. Moreover, the slow release components of the fertilizing composition exists in the form of particulates which are prone to be washed off or otherwise removed from the plant before degradation to assimilable compounds occurs. Even when the particulates remain adhered to the plant foliage during the degradation cycle, the resultant feeding sites are too scattered in distribution for the most effective feeding of the plant by this means.
The foremost object of this invention is accordingly that of designing a urea-formaldehyde fertilizer composition adapted for the foliar feeding of plants which substantially obviates the problems and disadvantages existing with the prior art practices in this regard.